A power convertor is configured by main circuit switching elements which are semiconductor elements (a module formed by a semiconductor switching element such as IGBT and a diode which is connected in reversely parallel to the semiconductor switching element; this is the same in the following description). As means for generating a high voltage in the power convertor, there is a circuit configuration in which a plurality of semiconductor elements are connected in series to each other.
A multilevel power convertor, like the above power convertor, which outputs five-level voltages in the circuit configuration in which the plurality of semiconductor elements are connected in series to each other, has been proposed. As one of configurations of the multilevel power convertor, a circuit configuration as disclosed in PATENT DOCUMENT 1 has been proposed. In PATENT DOCUMENT 1, as illustrated in FIG. 27 of the present application, DC voltage sources DCC1 and DCC2, and flying capacitors FC1 and FC2 are in common to three phases, and thus the number of capacitors used in the multilevel power convertor can be reduced, thereby allowing size reduction of the device.